b r – I’ve lived in plenty and restored plenty in my professional work. Whilst you’re right – stone is never going to achieve the same results as a modern build, it often performs much better than expected – especially if there is a rubble infill, which is often made up of lots of air, which breaks the direct heat loss path. Regardless, I would not advocate buying a Listed property with the expectation that you will be able to insulate through-out. If the OP is seriously considering insulating, read the listing documentation to see what is and isn’t covered, then speak with the local conservation officer, they may be receptive to the idea, but I doubt it.